The physical uplink channels of the Long Term Evolution (LTE for short) system comprise a physical random access channel (PRACH for short), a physical uplink shared channel (PUSCH for short), and a physical uplink control channel (PUCCH for short). In addition, there are two types of physical uplink signals, one type is demodulation reference signal (DMRS for short) for demodulating a data/control signaling, and the other type is sounding reference signal (SRS for short) for measuring an uplink channel. The PUSCH/PUCCH has two different types of cyclic prefix (CP for short) lengths, i.e. normal cyclic prefix (Normal CP for short) and extended cyclic prefix (Extended CP for short).
In the current LTE system, a physical uplink control information (Uplink Control Information, UCI for short) comprises an ACK/NACK, a channel state information (CSI, wherein the CSI includes: a Channel Quality Indicator (CQI), a Precoding Matrix Indicator (PMI) and Rank Indicator (RI)), and a scheduling request (SR) and a combination when they are simultaneously transmitted. It is also prescribed by the LTE that if there is no PUSCH transmission in the current subframe, one or more types of the UCIs above (only limited to combinations of two types of the UCIs) are transmitted on the PUCCH, and if there is PUSCH transmission in the current subframe, one or more types of the UCIs above are transmitted on the PUSCH together with the data.
The LTE defines multiple types of PUCCH format, including PUCCH format 1/1a/1b (a schematic diagram of channel structure thereof is as shown in FIG. 1) and format 2/2a/2b (a schematic diagram channel structure thereof is as shown in FIG. 2), wherein the format 1 is configured to transmit a scheduling request from a UE, the format 1a and format 1b are configured to feed back an 1-bit ACK/NACK and 2-bit ACK/NACK respectively, the format 2 is configured to transmit downlink channel state information, the format 2a is configured to transmit CSI information multiplexed with 1-bit ACK/NACK and the format 2b is configured to transmit CSI information multiplexed with 2-bit ACK/NACK.
In addition, in order to support the simultaneous transmission of the PUCCH format 1/1a/1b and an SRS, LTE also defines the shortened format of the PUCCH format 1/1a/1b, that is, the PUCCH is not configured to transmit the PUCCH on the last symbol of a subframe, and the last symbol of the subframe is configured to transmit the SRS. With respect to the shortened format, a format in which a last symbol of a subframe is configured to transmit the PUCCH is called a normal PUCCH format.
The SRS is a signal transmitted from the UE for the eNB to measure wireless the channel information (channel state information, CSI for short) by an eNB. In the LTE system, the UE transmits an uplink SRS periodically on the last symbol of a subframe according to parameters such as bandwidth, frequency domain location, sequence cyclic shift, period and subframe offset configured by an eNB. The eNB determines an uplink CSI of the UE according to a received SRS and performs operations such as frequency domain selection scheduling and closed-loop power control according to the obtained CSI. The LTE only supports periodic SRS. Therefore, in the following descriptions, the SRS always refers to periodic SRS if there is no specific instruction.
It is prescribed by the LTE that the SRS is transmitted on the last symbol of a subframe, and meanwhile, in order to maintain single-carrier properties of an uplink signal and avoid mutual interference between an SRS and a PUSCH/PUCCH of different UEs, the LTE makes the following regulations.
(1) When the UE needs to simultaneously transmit the PUSCH and the SRS on a certain subframe, the last symbol of the corresponding subframe does not transmit PUSCH, and the SRS is transmitted on the last symbol of the subframe.
(2) When the UE only needs to transmit the PUSCH on a certain subframe, if the subframe is higher layer configured as a cell-specific SRS subframe, then, when a resource allocation of the PUSCH partially overlaps with the higher layer configured cell-specific SRS bandwidth configuration, the last symbol of the subframe does not transmit the PUSCH; otherwise, the last symbol of the subframe transmits the PUSCH.
(3) When the UE needs to simultaneously transmit the PUCCH and the SRS on a certain subframe, if the PUCCH is of the PUCCH format 1/1a/1b, then, when a higher-layer configured parameter Simultaneous-AN-and-SRS is TRUE, the PUCCH is transmitted using a shortened format, and the SRS is transmitted on the last symbol of the subframe; otherwise, the PUCCH is transmitted using a normal format, and meanwhile, the SRS is skipped (that is to say, no SRS is transmitted on the current subframe).
(4) When the UE needs to simultaneously transmit the PUCCH and the SRS on a certain subframe, if the PUCCH is of the PUCCH format 2/2a/2b, then, the UE only transmits the PUCCH, and meanwhile, the SRS is skipped.
In an International Mobile Telecommunications-Advanced (IMT-Advanced for short) system, a high-speed transmission of data can be realized, and there is a quite large system capacity. A peak rate of the IMT-Advanced system can reach 1 Gbit/s in a situation of low-speed movement and hot-spot coverage, and 100 Mbit/s in a situation of high-speed movement and wide Area coverage.
In order to satisfy requirements of the International Telecommunication Union-Advanced (ITU-Advanced for short), the Long Term Evolution Advanced (LTE-A for short) system, as the evolution standard of the LTE, should support wider system bandwidths (up to 100 MHz), and also needs to be backward compatible with the existing standards of the LTE. On the basis of the existing LTE system, the bandwidths of the LTE system can be combined to obtain a wider bandwidth, which technology is called carrier aggregation (CA for short) technology. This technology is capable of enhancing the frequency spectrum utilization of the IMT-Advance system, relieving the shortage of the frequency spectrum resources and further optimizing the utilization of the frequency spectrum resources.
In a system to which the CA is introduced, a carrier performing aggregation is called a Component Carrier (CC for short), and is also called a cell. Moreover, concepts of primary component carrier/cell (PCC/PCell for short) and secondary component carrier/cell (SCC/SCell for short) are also put forward. A system having performed the CA at least comprises one primary component carrier and one secondary component carrier, wherein the primary component carrier is always in an activation state. In the following descriptions, the component carrier and the cell are equivalent.
After the introduction of the CA, in the current discussion about relationships among a downlink component carrier, a PDSCH transmission block and a HARQ process, one basic working assumption is that when no space division multiplexing is used, one downlink component carrier is corresponding to one PDSCH transmission block and one HARQ process, that is to say, the UE needs to feed back a 1-bit ACK/NACK for one PDSCH transmission block of each component carrier. When the space division multiplexing is used, it is currently prescribed by the LTE-A that at most two transmission blocks are supported. As a result, when the space division multiplexing is used, the UE needs to feed back a 2-bit ACK/NACK for two PDSCH transmission blocks of each downlink component carrier.
In an LTE-A system in which the frequency spectrum aggregation technology is used, the uplink bandwidth and the downlink bandwidth can comprise a plurality of component carriers. When an eNB has PDSCHs on a plurality of downlink component carriers to be scheduled to a certain UE, and when the UE has no PUSCH to be transmitted in a current subframe, a terminal should feedback the ACK/NACK for the PDSCHs of the plurality of downlink component carriers on the PUCCH. A current working assumption is that these ACK/NACK are transmitted on one UE-specific uplink component carrier; as for SR information, a current working assumption is that the UE only transmits one SR, and the SR information is transmitted on one UE-specific uplink component carrier; and as for CSI information, a current working assumption is that the CSI information is transmitted on one UE-specific uplink component carrier.
In the LTE-A system, a current working assumption is that the UE transmits the SR information by using the PUCCH format 1, and the UE transmits the CSI by using the PUCCH format 2. As for the ACK/NACK, it can be transmitted not only by the PUCCH format 1a, 1b and multiplexing with channel selection, which have been already defined in LTE, but also by a new DFT-s-OFDM-based format, which is added to the LTE-A for transmitting ACK/NACK with a larger payload, and the channel structure schematic diagram of the DFT-s-OFDM-based format is as shown in FIG. 3. For the sake of convenient description, this format is called PUCCH Format 3. For a UE that at most can support a 4-bit ACK/NACK feedback, the ACK/NACK thereof will be fed back in a manner of the PUCCH format 1b with channel selection, and for a high-end UE that can support more than 4 bits ACK/NACK feedback, the mode in which the UE feeds back the ACK/NACK is configured by higher-layer signaling.
Apart from the CA technology, an uplink multi-antenna is also introduced into the LTE-A, and at most four antennas can be configured as uplink transmitting antennas. Therefore, in order to obtain the channel state information of each uplink transmitting antenna, the UE needs to simultaneously transmit the SRS on multiple antennas.
It is put forward in the existing LTE-A research that in the uplink communication, non-precoded (i.e. antenna-specific) SRS should be used, and the DMRS of the PUSCH should be precoded. The eNB can get an estimate of an original CSI of the uplink by receiving the non-precoded SRS, and the DMRS that has been precoded cannot enable the eNB to get an estimate of the original CSI of the uplink. At this time, when the UE transmits the non-precoded SRS by using multiple antennas, SRS resources needed by each UE are increased, which also results in decrease of the number of UEs that can be simultaneously multiplexed in the system. Besides, apart from retaining the original periodic transmission of the SRS of the LTE, in order to improve the utilization ratio of the SRS resources and enhance the flexibility of the resource scheduling, the SRS also can be transmitted aperiodically via downlink control information or higher-layer signaling for a UE.
In the LTE-A, in order to make full use of the uplink resources and consider the generally good channel quality in an application scenario of the carrier aggregation, requirements to the single carrier properties of the uplink signal are relaxed, and the PUCCH and the PUSCH are allowed to be simultaneously transmitted. Whether to allow the UE to simultaneously transmit the PUCCH and the PUSCH or not can be configured with higher-layer parameters.
Therefore, in the LTE-A system, when confronted with introduction of various novel technologies, such as CA, uplink multi-antenna, PUCCH format 3, aperiodic SRS and simultaneous transmission of the PUCCH and the PUSCH, the existing UE cannot realize simultaneous transmission of a plurality of types of physical uplink signals/channels.